in the Museum of St, Bartkoiomew's Hospital, 417 



phate. From several facts which I have observed, I am, 'how- 

 ever, convinced that the relative proportions of a^id and 

 base in the phosphate of hme surrounding other calcuh*, 

 whether alone or mixed with the phosphate of ammonia 

 and magnesia, varies considerably : and whether this arises 

 from a mixture of two or more of the already known com- 

 pounds of lime and phosphoric acid, or whether they are 

 definite compounds of which we have at present no know- 

 ledge, I am unable to decide, although I believe the latter 

 may occasionally be the case. In a calculus which consisted 

 of urate of ammonia and oxalate of lime surrounded by the 

 mixed phosphate, was observed among the latter a layer 

 which had an imperfectly fibrous structure and was much 

 harder in texture and more compact than the rest : on di- 

 gesting a portion of this in dilute acetic acid effervescence 

 took place and some lime was dissolved ; the insoluble matter 

 left had a crystalline appearance, and was found to be phos- 

 phate of lime. When dissolved in stronger acid and the so- 

 lution neutralized by ammonia a gelatinous precipitate fell, 

 which after standing about four and twenty hours was wholly 

 converted into a number of small crystals, having undergone 

 similar changes to freshly precipitated uric acid. If these 

 crystals are left for a few days in the solution from which they 

 have been thrown down, they gradually disappear, and are 

 reconverted into an amorphous precipitate, differing only from 

 the former in not being quite so gelatinous. The nature of the 

 changes which take place I am unable at present to explain, 

 although 1 find that when the diphosphate of lime (prepared 

 by dropping a solution of phosphate of soda into one of mu- 

 riate of lime, the latter being in excess,) is precipitated from 

 its acetic solution, the same appearances present themselves : 

 the conversion is, however, only partial. The calculi which 

 contain this phosphate usually partake more or less of the 

 external characters before mentioned ; in some of them it ap- 

 peared to be mixed with the bone-earth phosphate, properly 

 so called. If it be identical in composition with the diphos- 

 phate, which I believe to be the case, the property alluded to 

 is not noticed in any of the chemical works I have consulted. 

 I am informed by Dr. Prout, that he has remarked the same. 

 Only in one instance have I seen the radiated structure noticed 

 by Dr. Wollaston ; it formed a thin layer among the mixed 

 phosphates, surrounding a calculus of oxalate of lime. 



Phosphate of Magnesia and Ammonia. — This specimen has 

 not been divided; it probably contains a nucleus of uric acid, 

 and should therefore have been arranged among the alter- 

 nating calculi. 



PhiLMag. 5.3. Vol. 12. No. 76. Mai/ 1838. 5i O 



